[Dnsmasq-discuss] Option 12 hostname sent to RPi seems incorrect
Geert Stappers
stappers at stappers.nl
Wed Oct 20 21:32:31 UTC 2021
On Wed, Oct 20, 2021 at 10:56:02PM +0200, Geert Stappers wrote:
> On Wed, Oct 20, 2021 at 02:48:27PM +0530, Shrenik Bhura wrote:
> > On Wed, 20 Oct, 2021, 11:21 Geert Stappers wrote:
> > > On Wed, Oct 20, 2021 at 07:50:58AM +0530, Shrenik Bhura wrote:
> > > > There isn't anything specific in the configuration that serves the
> > > > hostname. I am aware of this feature and when defined it works as desired.
> > > > But when nothing is explicitly defined to serve hostnames, it is defaulting
> > > > to 192 as visible in the logs, and only in the case of an RPi.
> > > > When checked on the client with the hostname command, it shows the full
> > > > hostname - 192.168.67.53
> > >
> > > Such hostname do I call IPaddress.
> > >
> > >
> > > > The same configuration works fine with a x86 system as no hostname is being
> > > > served when none is defined.
Yes, dnsmasq works great.
> > > > Have attached the config files involved.
> > >
> > > Make a packet capture and put the .pcap on a server.
> > > Then tell here how to fetch the file.
> > > Next can those who care examine the .pcap with their tool.
> > > (wireshark / tcpdump)
> > >
> > > > Once again, do note that this is the case only for an RPi. So there is some
> > > > specific logic in dnsmasq coming into play for an RPi that seems to be
> > > > serving the IP address as the default hostname when none is present.
> > >
> > > So beside the
> > > /sbin/tcpdump -w rpi.pcap ether host dc:a6:32:78:98:ae
> > > also
> > > /sbin/tcpdump -w worksfine.pcap ether host MAC_address_of_known_good
> > >
> >
> > Herein is the link to the related packet captures of an RPi and x86 system
> > -
> > https://drive.google.com/file/d/11RwpCdbE8W0ohS2QDj4BarZ_VHnEhwfs/view?usp=sharing
> >
>
> The "works fine" is/was captured different as the Raspi capture.
> Luckly is the Raspi packet capture the better one, it contains replies.
>
> What `tshark` says about it.
> Note the packet count and the time offset (columns 1 and 2)
> and that there are three transactions.
>
>
> |$ tshark -nr rpi.pcap | grep DHCP
> | 1 0.000000 0.0.0.0 → 255.255.255.255 DHCP 364 DHCP Discover - Transaction ID 0x6e9ddeb7
> | 2 0.001666 192.168.67.1 → 192.168.67.53 DHCP 425 DHCP Offer - Transaction ID 0x6e9ddeb7
> | 3 0.059905 0.0.0.0 → 255.255.255.255 DHCP 351 DHCP Request - Transaction ID 0x6e9ddeb7
> | 7 0.106212 192.168.67.1 → 192.168.67.53 DHCP 344 DHCP ACK - Transaction ID 0x6e9ddeb7
> |119315 40.665138 0.0.0.0 → 255.255.255.255 DHCP 590 DHCP Discover - Transaction ID 0x378f8d8b
> |119316 40.668636 192.168.67.1 → 192.168.67.53 DHCP 342 DHCP Offer - Transaction ID 0x378f8d8b
> |119317 40.673119 0.0.0.0 → 255.255.255.255 DHCP 590 DHCP Request - Transaction ID 0x378f8d8b
> |119318 40.727456 192.168.67.1 → 192.168.67.53 DHCP 342 DHCP ACK - Transaction ID 0x378f8d8b
> |119324 44.861769 0.0.0.0 → 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x6f84b210
> |119325 44.866031 192.168.67.1 → 192.168.67.53 DHCP 342 DHCP Offer - Transaction ID 0x6f84b210
> |119326 44.866612 0.0.0.0 → 255.255.255.255 DHCP 342 DHCP Request - Transaction ID 0x6f84b210
> |119327 44.911006 192.168.67.1 → 192.168.67.53 DHCP 343 DHCP ACK - Transaction ID 0x6f84b210
> |$
>
>
> Tcpdump Verbose, `-v`, of that:
>
> $ tcpdump -nr rpi.pcap -v port bootpc
> reading from file rpi.pcap, link-type EN10MB (Ethernet), snapshot length 262144
> 10:48:00.072173 IP (tos 0x0, ttl 64, id 20588, offset 0, flags [none], proto UDP (17), length 350)
> 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from dc:a6:32:78:98:ae, length 322, xid 0x6e9ddeb7, Flags [none]
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: Discover
DHCP Discover
> Parameter-Request (55), length 14:
> Subnet-Mask (1), Default-Gateway (3), Vendor-Option (43), Vendor-Class (60)
> TFTP (66), BF (67), Unknown (128), Unknown (129)
> Unknown (130), Unknown (131), Unknown (132), Unknown (133)
> Unknown (134), Unknown (135)
> Vendor-Class (60), length 32: "PXEClient:Arch:00000:UNDI:002001"
> ARCH (93), length 2: 0
And ARCH 0 is "PC" ...
> NDI (94), length 3: 1.2.1
> GUID (97), length 17: 0.82.80.105.52.18.49.192.0.50.120.152.174.94.119.158.94
> 10:48:00.073839 IP (tos 0xc0, ttl 64, id 5852, offset 0, flags [none], proto UDP (17), length 411)
> 192.168.67.1.67 > 192.168.67.53.68: BOOTP/DHCP, Reply, length 383, xid 0x6e9ddeb7, Flags [none]
> Your-IP 192.168.67.53
> Server-IP 192.168.67.1
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: Offer
DHCP Offer
> Server-ID (54), length 4: 192.168.67.1
> Lease-Time (51), length 4: 43200
> BF (67), length 19: "ltsp/undionly.kpxe^@"
> RN (58), length 4: 21600
> RB (59), length 4: 37800
> Subnet-Mask (1), length 4: 255.255.255.0
> BR (28), length 4: 192.168.67.255
> Default-Gateway (3), length 4: 192.168.67.1
> Vendor-Class (60), length 9: "PXEClient"
> GUID (97), length 17: 0.82.80.105.52.18.49.192.0.50.120.152.174.94.119.158.94
> Vendor-Option (43), length 44: 6.1.3.10.4.0.80.88.69.8.7.128.4.1.192.168.67.1.9.23.128.4.20.82.97.115.112.98.101.114.114.121.32.80.105.32.66.111.111.116.32.32.32.255
> 10:48:00.132078 IP (tos 0x0, ttl 64, id 20590, offset 0, flags [none], proto UDP (17), length 337)
> 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from dc:a6:32:78:98:ae, length 309, xid 0x6e9ddeb7, Flags [none]
> Server-IP 192.168.67.1
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: Request
DHCP Request
> Requested-IP (50), length 4: 192.168.67.53
> Server-ID (54), length 4: 192.168.67.1
> Vendor-Class (60), length 32: "PXEClient:Arch:00000:UNDI:002001"
> GUID (97), length 17: 0.82.80.105.52.18.49.192.0.50.120.152.174.94.119.158.94
> 10:48:00.178385 IP (tos 0xc0, ttl 64, id 5869, offset 0, flags [none], proto UDP (17), length 330)
> 192.168.67.1.67 > 192.168.67.53.68: BOOTP/DHCP, Reply, length 302, xid 0x6e9ddeb7, Flags [none]
> Your-IP 192.168.67.53
> Server-IP 192.168.67.1
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: ACK
DHCP Acknowledge
> Server-ID (54), length 4: 192.168.67.1
> Lease-Time (51), length 4: 43200
> RN (58), length 4: 21600
> RB (59), length 4: 37800
> Subnet-Mask (1), length 4: 255.255.255.0
> BR (28), length 4: 192.168.67.255
> Default-Gateway (3), length 4: 192.168.67.1
> LOG (7), length 4: 192.168.67.1
> Domain-Name-Server (6), length 8: 8.8.8.8,8.8.8.8
First "DHCP Cycle" is complete.
Next DHCP Cycle starts.
> 10:48:40.737311 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 576)
> 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from dc:a6:32:78:98:ae, length 548, xid 0x378f8d8b, Flags [none]
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: Discover
DHCP Discover
> Parameter-Request (55), length 9:
> Subnet-Mask (1), Default-Gateway (3), Domain-Name-Server (6), Hostname (12)
> Domain-Name (15), RP (17), MTU (26), YD (40)
> NTP (42)
> 10:48:40.740809 IP (tos 0xc0, ttl 64, id 3785, offset 0, flags [none], proto UDP (17), length 328)
> 192.168.67.1.67 > 192.168.67.53.68: BOOTP/DHCP, Reply, length 300, xid 0x378f8d8b, Flags [none]
> Your-IP 192.168.67.53
> Server-IP 192.168.67.1
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: Offer
DHCP Offer
> Server-ID (54), length 4: 192.168.67.1
> Lease-Time (51), length 4: 43200
> RN (58), length 4: 21600
> RB (59), length 4: 37800
> Subnet-Mask (1), length 4: 255.255.255.0
> BR (28), length 4: 192.168.67.255
> Default-Gateway (3), length 4: 192.168.67.1
> Domain-Name-Server (6), length 8: 8.8.8.8,8.8.8.8
> 10:48:40.745292 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 576)
> 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from dc:a6:32:78:98:ae, length 548, xid 0x378f8d8b, Flags [none]
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: Request
DHCP Request
> Server-ID (54), length 4: 192.168.67.1
> Requested-IP (50), length 4: 192.168.67.53
> Parameter-Request (55), length 9:
> Subnet-Mask (1), Default-Gateway (3), Domain-Name-Server (6), Hostname (12)
> Domain-Name (15), RP (17), MTU (26), YD (40)
> NTP (42)
> 10:48:40.799629 IP (tos 0xc0, ttl 64, id 3788, offset 0, flags [none], proto UDP (17), length 328)
> 192.168.67.1.67 > 192.168.67.53.68: BOOTP/DHCP, Reply, length 300, xid 0x378f8d8b, Flags [none]
> Your-IP 192.168.67.53
> Server-IP 192.168.67.1
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: ACK
DHCP Acknowledge
> Server-ID (54), length 4: 192.168.67.1
> Lease-Time (51), length 4: 43200
> RN (58), length 4: 21600
> RB (59), length 4: 37800
> Subnet-Mask (1), length 4: 255.255.255.0
> BR (28), length 4: 192.168.67.255
> Default-Gateway (3), length 4: 192.168.67.1
> Domain-Name-Server (6), length 8: 8.8.8.8,8.8.8.8
Second "DHCP Cycle" is complete.
> |119318 40.727456 192.168.67.1 → 192.168.67.53 DHCP 342 DHCP ACK - Transaction ID 0x378f8d8b
> } Five ICMPv6 packets
> |119324 44.861769 0.0.0.0 → 255.255.255.255 DHCP 342 DHCP Discover - Transaction ID 0x6f84b210
Next DHCP Cycle starts.
> 10:48:44.933942 IP (tos 0x10, ttl 128, id 0, offset 0, flags [none], proto UDP (17), length 328)
> 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from dc:a6:32:78:98:ae, length 300, xid 0x6f84b210, Flags [none]
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: Discover
DHCP Discover
> Hostname (12), length 13: "192.168.67.53"
Client says "My hostname is '192.168.67.53'"
> Parameter-Request (55), length 13:
> Subnet-Mask (1), BR (28), Time-Zone (2), Default-Gateway (3)
> Domain-Name (15), Domain-Name-Server (6), Unknown (119), Hostname (12)
> Netbios-Name-Server (44), Netbios-Scope (47), MTU (26), Classless-Static-Route (121)
> NTP (42)
> 10:48:44.938204 IP (tos 0xc0, ttl 64, id 3933, offset 0, flags [none], proto UDP (17), length 328)
> 192.168.67.1.67 > 192.168.67.53.68: BOOTP/DHCP, Reply, length 300, xid 0x6f84b210, Flags [none]
> Your-IP 192.168.67.53
> Server-IP 192.168.67.1
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: Offer
DHCP Offer
> Server-ID (54), length 4: 192.168.67.1
> Lease-Time (51), length 4: 43200
> RN (58), length 4: 21600
> RB (59), length 4: 37800
> Subnet-Mask (1), length 4: 255.255.255.0
> BR (28), length 4: 192.168.67.255
> Default-Gateway (3), length 4: 192.168.67.1
> Domain-Name-Server (6), length 8: 8.8.8.8,8.8.8.8
> 10:48:44.938785 IP (tos 0x10, ttl 128, id 0, offset 0, flags [none], proto UDP (17), length 328)
> 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from dc:a6:32:78:98:ae, length 300, xid 0x6f84b210, Flags [none]
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: Request
DHCP Request
> Server-ID (54), length 4: 192.168.67.1
> Requested-IP (50), length 4: 192.168.67.53
> Hostname (12), length 13: "192.168.67.53"
Client says "My hostname is '192.168.67.53'"
> Parameter-Request (55), length 13:
> Subnet-Mask (1), BR (28), Time-Zone (2), Default-Gateway (3)
> Domain-Name (15), Domain-Name-Server (6), Unknown (119), Hostname (12)
> Netbios-Name-Server (44), Netbios-Scope (47), MTU (26), Classless-Static-Route (121)
> NTP (42)
> 10:48:44.983179 IP (tos 0xc0, ttl 64, id 3934, offset 0, flags [none], proto UDP (17), length 329)
> 192.168.67.1.67 > 192.168.67.53.68: BOOTP/DHCP, Reply, length 301, xid 0x6f84b210, Flags [none]
> Your-IP 192.168.67.53
> Server-IP 192.168.67.1
> Client-Ethernet-Address dc:a6:32:78:98:ae
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message (53), length 1: ACK
DHCP Acknowledge
> Server-ID (54), length 4: 192.168.67.1
> Lease-Time (51), length 4: 43200
> RN (58), length 4: 21600
> RB (59), length 4: 37800
> Subnet-Mask (1), length 4: 255.255.255.0
> BR (28), length 4: 192.168.67.255
> Default-Gateway (3), length 4: 192.168.67.1
> Hostname (12), length 3: "192"
Server says "Your hostname is '192'"
> Domain-Name-Server (6), length 8: 8.8.8.8,8.8.8.8
>
>
> More in the next message.
Done "in line"
Back to:
> > > On Wed, Oct 20, 2021 at 07:50:58AM +0530, Shrenik Bhura wrote:
> > > > There isn't anything specific in the configuration that serves the
> > > > hostname. I am aware of this feature and when defined it works as desired.
Acknowledge on "it works as desired".
> > > > But when nothing is explicitly defined to serve hostnames,
> > > > it is defaulting to 192 as visible in the logs,
There I tent to disagree.
> > > > and only in the case of an RPi.
I do read that as
"There are some more factors. There are yet unknown factors."
> > > > When checked on the client with the hostname command,
> > > > it shows the full hostname - 192.168.67.53
Yes. And the question is: How did it get there?
Groeten
Geert Stappers
--
Silence is hard to parse
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